Nervous System 2- CNS4.pdf

Learning Objectives The Central Nervous System The Brain Identify and describe the major structures and regions of the brain, and their functions (e.g., cerebrum, cerebellum, thalamus, hypothalamus, pons, medulla). List the four lobes of the cerebral cortex and describe the major function(s)...

Learning Objectives The Central Nervous System The Brain Identify and describe the major structures and regions of the brain, and their functions (e.g., cerebrum, cerebellum, thalamus, hypothalamus, pons, medulla). List the four lobes of the cerebral cortex and describe the major function(s) of each lobe (e.g., occipital lobe is associated with vision). List the major functions of the diencephalon, and name its subdivisions and functions. Identify the three major regions of the brain stem, and note the functions of each area. Protection of the Brain Describe how meninges, cerebrospinal fluid, and the blood brain barrier protect the CNS. The Spinal Cord Label or describe a cross-sectional view of the spinal cord to show the locations and functions of major structures (e.g., spinal nerves, gray matter, white matter, dorsal root ganglion). Define ascending and descending spinal cord tracts, and describe the structure, location, and function of each. 1 Brain structure and functions Brain The brain contains centers that control breathing, blood pressure, heart rate, digestion, gland secretion, level of alertness and ability to sleep - all vital activity necessary to survive. It is the centre of consciousness, intellect, memory, language and cognition, receiving and interpreting sensory information and controlling movement. It also contains reflex centers that control swallowing, coughing, sneezing and vomiting. It is responsible for co-ordination, and maintaining of posture, muscle tone, and balance. Brain Regions and Organization Adult brains have four regions: 1. Cerebral hemispheres (cortex (gray matter), white matter and basal nuclei 2. Diencephalon- (thalamus, hypothalamus, epithalamus) 3. Brain stem, consisting of: Midbrain Pons Medulla 4. Cerebellum © 2016 Pearson Education, Ltd. Brain Cerebral hemisphere Diencephalon Cerebellum Brain stem Midbrain Pons Medulla oblongata Birth: Shows adult pattern of structures and convolutions. © 2016 Pearson Education, Ltd. Brain Regions and Organization (cont.) Gray matter: short, nonmyelinated neurons and cell bodies White matter: myelinated and nonmyelinated axons Basic pattern found in CNS: central cavity surrounded by gray matter, with white matter external to gray matter Features and changes of pattern: 1. Spinal cord exhibits this basic pattern; however, pattern changes with ascent into brain stem 2. Brain stem has additional gray matter nuclei scattered within white matter 3. Cerebral hemispheres (cerebrum) and cerebellum contain outer layer of gray matter called the cortex Cerebrum and cerebellum also have scattered areas of gray matter nuclei amid white matter © 2016 Pearson Education, Ltd. Ventricles Fluid-filled chambers that are continuous to one another and to central canal of spinal cord Filled with cerebrospinal fluid (CSF) Lined by ependymal cells (neuroglial cells) Paired lateral ventricles are large, C-shaped chambers located deep in each hemisphere Lateral ventricle Anterior horn Septum Posterior pellucidum horn Interventricular foramen Inferior Inferior horn horn Third ventricle Lateral Lateral Cerebral aqueduct aperture aperture Fourth ventricle Median Central canal aperture Anterior view Left lateral view © 2016 Pearson Education, Ltd. 12.2 Cerebral Hemispheres Cerebral hemispheres form superior part of brain Account for 83% of brain mass Surface markings: Gyri: ridges Sulci: shallow grooves Fissures: deep grooves Longitudinal fissure Separates two hemispheres Transverse cerebral fissure Separates cerebrum and cerebellum © 2016 Pearson Education, Ltd. Brain Lobes Contain elevated ridges (gyri) and shallow grooves (sulci). Deep sulci divide the hemispheres into lobes: Frontal, Parietal, Temporal, Occipital,  Figure 12.6a Functional and structural areas of the cerebral cortex. Motor areas Central sulcus Sensory areas and related Primary motor cortex association areas Primary somatosensory Premotor cortex cortex Somatic Frontal Somatosensory sensation eye field association cortex Broca's area Gustatory cortex (outlined by dashes) Taste (in insula) Prefrontal cortex Working memory Wernicke's area for spatial tasks (outlined by dashes) Executive area for task management Working memory for Primary visual object-recall tasks cortex Visual Vision Solving complex, multitask problems association area Auditory association area Hearing Primary auditory cortex Lateral view, left cerebral hemisphere Primary motor Motor association Primary sensory Sensory Multimodal association cortex cortex cortex association cortex cortex © 2013 Pearson Education, Inc. Table 14–3 The Cerebral Cortex 11 © 2018 Pearson Education, Ltd. 4 General Considerations of Cerebral Cortex 1. Three types of functional areas Motor areas—control voluntary movement Sensory areas—conscious awareness of sensation Association areas—integrate diverse information 2. Each hemisphere concerned with contralateral side of body 3. Lateralization of cortical function in hemispheres 4. Conscious behavior involves entire cortex in some way © 2013 Pearson Education, Inc.  Sensory and Motor Areas of the Cerebral Cortex Figure 7.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.31 Cerebral Cortex (cont.) Lateralization of cortical functioning Left hemisphere Controls language, math, and logic Right hemisphere Visual-spatial skills, intuition, emotion, and artistic and musical skills Hemispheres communicate almost instantaneously via fiber tracts and functional integration © 2016 Pearson Education, Ltd. 15 Protection of the Brain The brain is protected by: bone, meninges, cerebrospinal fluid. Harmful substances are shielded from the brain by the blood-brain barrier.  Protective structures of the brain Protective structures Bone, meninges, cerebrospinal fluid, blood-brain barrier of the brain Meninges: dura mater, Cover and protect the CNS arachnoid mater, pia Protect blood vessels and enclose venous sinuses mater Contain cerebrospinal fluid (CSF) Form partitions within the skull Cerebrospinal Fluid Forms a liquid cushion to the CNS organs Nourishes the brain and carries chemical signals throughout it Choroid plexus Produces Cerebrospinal Fluid (capillary and ependymal cells) Ventricles of the Hollow chambers filled with cerebrospinal fluid and lined by ependymal Brain (4) cells. The blood-brain Maintains stable environment in the brain: restricts the passage of large barrier (endothelial molecules and bacteria into the CSF; allows the diffusion of small cells and associated molecules (O2, hormones, CO2, glucose, amino acids, electrolytes). astrocytes) Alcohol, nicotine, anesthetics can pass through the BBB 12.10 Spinal Cord Gross Anatomy and Protection Spinal cord is enclosed in vertebral column Begins at the foramen magnum Ends at L1 or L2 vertebra Functions Provides two-way communication to and from brain and body Major reflex center: reflexes are initiated and completed at spinal cord © 2016 Pearson Education, Ltd. Figure 13–2ab Gross Anatomy of the Adult Spinal Cord. C1 KEY C2 Spinal cord and vetebral regions C3 Spinal cord = Cervical C4 C1 = Thoracic C5 C2 Vertebrae Cervical C3 = Lumbar C6 spinal C4 C5 = Sacral C7 nerves C6 C7 Cervical C8 enlargement C8 T1 T1 T2 T2 T3 T3 T4 T5 T4 T6 T5 T7 Thoracic T8 T6 Posterior spinal median sulcus T7 nerves T9 T10 T8 T11 Lumbosacral T9 T12 enlargement Conus T10 L1 medullaris T11 L2 Inferior T12 Lumbar L3 tip of spinal spinal cord L1 KEY nerves L4 Cauda equina Spinal cord and vetebral regions L5 L2 = Cervical = Thoracic S1 L3 = Lumbar Sacral spinal nerves S2 = Sacral S3 L4 S4 S5 L5 Coccygeal Filum terminale nerve (Co1) (in coccygeal S1 ligament) S2 S3 S4 S5 a The superficial anatomy and orientation of the Co1 adult spinal cord. The numbers to the left identify the spinal nerves and indicate where the b Lateral view of adult vertebrae nerve roots leave the vertebral canal. The adult and spinal cord. Note that the spinal cord extends from the brain only to the spinal cord segments for level of vertebrae L1–L2; the spinal segments found at representative locations are indicated in S1–S5 are level with the T12–L1 the cross sections. vertebrae. 19 © 2018 Pearson Education, Ltd. Gross Anatomy and Protection (cont.) Protected by bone, meninges, and CSF Spinal dura mater is one layer thick Does not attach to vertebrae Epidural space Cushion of fat and network of veins in space between vertebrae and spinal dura mater CSF fills subarachnoid space between arachnoid and pia maters Dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2 Site of lumbar puncture or tap © 2016 Pearson Education, Ltd. ure 12.28 Diagram of a lumbar puncture. T12 L5 Ligamentum flavum Lumbar puncture needle entering subarachnoid space L4 Supra- spinous ligament L5 Filum terminale S1 Inter- Cauda equina vertebral Arachnoid DuraLtd. © 2016 Pearson Education, in subarachnoid disc mater mater space Spinal Cord Cross-sectional Anatomy (cont.) Gray matter and spinal roots (cont.) Gray commissure: bridge of gray matter that connects masses of gray matter on either side Encloses central canal Ventral roots: bundle of motor neuron axons that exit the spinal cord Dorsal roots: sensory input to cord Dorsal root (spinal) ganglia: cell bodies of sensory neurons Spinal nerves: formed by fusion of dorsal and ventral roots © 2016 Pearson Education, Ltd. Figure 12.30 Organization of the gray matter of the spinal cord. Dorsal root Dorsal horn (interneurons) (sensory) Dorsal root Somatic sensory ganglion SS neuron VS Visceral sensory VM neuron SM Visceral motor neuron Somatic motor neuron Spinal nerve Ventral horn Ventral root (motor neurons) (motor) SS Interneurons receiving input from somatic sensory neurons VS Interneurons receiving input from visceral sensory neurons VM Visceral motor (autonomic) neurons SM Somatic motor neurons © 2016 Pearson Education, Ltd. Spinal Cord Trauma Traumatic injury of vertebral and neural tissues due to compressing, pulling, or shearing forces. Most common locations: cervical (1, 2, 4-7), and T1–L2 lumbar vertebrae: the most mobile portions of vertebral column in these locations the spinal cord occupies most of the vertebral canal. The higher up the level of the injury -the more severe symptoms. Spinal Cord Injury (Cont’d) The level of injury is very helpful in predicting what parts of the body might be affected by paralysis and loss of function Cervical (neck) injuries usually result in Quadriplegia/Tetraplegia or fatal in instances. Paralysis of all four extremities Injuries to the spinal cord segments above the C4 level (C1,C2, C3) may result in the need of breathing aids such as mechanical ventilators or diaphragm pacemakers to simulate the phrenic nerve to initiate a persons breathing due to weak innervation of the diaphragm. Paraplegia Paralysis of the lower part of the trunk and legs 25 12.11 Neuronal Pathways Major spinal tracts are part of multineuron pathways Four key points about spinal tracts and pathways: Decussation: Most pathways cross from one side of CNS to other at some point Relay: Consist of chain of two or three neurons Somatotopy: precise spatial relationship in CNS correspond to spatial relationship in body Symmetry: pathways are paired symmetrically (right and left) © 2016 Pearson Education, Ltd. Ascending Pathways Conduct sensory pathways upward through a chain of three neurons: First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as it enters spinal cord or medulla Synapses with second-order neuron Second-order neuron Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum Third-order neuron Cell bodies in thalamus Axon extends to somatosensory cortex No third-order neurons in cerebellum © 2016 Pearson Education, Ltd. Ascending Pathways (cont.) Somatosensory signals travel along three main pathways on each side of spinal cord: Two pathways transmit somatosensory information to sensory cortex via thalamus Dorsal column–medial lemniscal pathways-Transmit input to somatosensory cortex for discriminative touch and vibrations Spinothalamic pathways-Transmit pain, temperature, coarse touch, and pressure impulses within lateral spinothalamic tract Third pathway, spinocerebellar tracts, terminate in the cerebellum © 2016 Pearson Education, Ltd. Figure 12.32b Pathways of selected ascending spinal cord tracts. Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature Lumbar spinal cord receptors Spinothalamic pathway © 2016 Pearson Education, Ltd. Descending Pathways and Tracts Deliver efferent impulses from brain to spinal cord Two groups Direct pathways: pyramidal tracts Indirect pathways: all others Motor pathways involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles © 2016 Pearson Education, Ltd.